Composite materials such as fiber-reinforced plastics (FRP) are lightweight and very strong, and are therefore widely used as structural members for aircraft, automobiles, and ships and the like. One example of a molding method for composite materials is the resin transfer molding (RTM) method. The RTM molding method is a molding method that involves placing a fiber-reinforced base material inside a male/female pair of molding dies, fastening the dies and evacuating the inside of the dies to a state of reduced pressure, and then injecting a resin into the inside of the dies through a resin injection port, thereby impregnating the fiber-reinforced base material with the resin:
As illustrated in FIG. 9, in a typical RTM molding method, the resin is injected from a resin injection line 2 provided at one end of the device, flows through the inside of a fiber-reinforced base material 11 in an in-plane direction, and is discharged from a suction line 3 provided at the opposite end of the device. In the RTM molding method, because the resin flows through the inside of the fiber-reinforced base material, low viscosity and high fluidity are essential characteristics for the resin.
The RTM method offers the advantage that molding can be performed with an extremely high level of shape precision. However, in the RTM molding method described above, because the resin is impregnated from one end of the fiber-reinforced base material through to the opposite end, if the member is increased in size and/or thickness, problems may arise, including the resin impregnation requiring a very long period of time, and the occurrence of non-impregnated regions. If the injection pressure is increased in order to raise the resin injection rate with the aim of shortening the impregnation time, then pressure loss increases, and there is a possibility that this may cause wrinkling of the fibers.
In order to address the problems mentioned above, methods such as those illustrated in FIG. 10 and FIG. 11 have been proposed, in which the resin impregnation is performed through the thickness direction. FIG. 10 is a method in which a plurality of injection ports are positioned in the upper die, and the resin is supplied to the fiber-reinforced base material through these ports, thereby impregnating the fiber-reinforced base material in the thickness direction. FIG. 11 is a method in which a porous plate 41 and an intermediate member 40 are placed on top of the fiber-reinforced base material, and impregnation is performed in the thickness direction across substantially the entire surface of the fiber-reinforced base material. A perforated resin film or the like is used as the intermediate member 40.